21515531221021 has 2 divisors, whose sum is σ = 21515531221022. Its totient is φ = 21515531221020.

The previous prime is 21515531220991. The next prime is 21515531221027. The reversal of 21515531221021 is 12012213551512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20369100609796 + 1146430611225 = 4513214^2 + 1070715^2 .

It is a cyclic number.

It is not a de Polignac number, because 21515531221021 - 2¹⁵ = 21515531188253 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21515531221027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10757765610510 + 10757765610511.

It is an arithmetic number, because the mean of its divisors is an integer number (10757765610511).

Almost surely, 2^{21515531221021} is an apocalyptic number.

It is an amenable number.

21515531221021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21515531221021 is an equidigital number, since it uses as much as digits as its factorization.

21515531221021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6000, while the sum is 31.

Adding to 21515531221021 its reverse (12012213551512), we get a palindrome (33527744772533).

The spelling of 21515531221021 in words is "twenty-one trillion, five hundred fifteen billion, five hundred thirty-one million, two hundred twenty-one thousand, twenty-one".